Variable-capacity compressed-air engine.



B. v. NORDBERG. VARIABLE CAPACITY COMPRESSED AIR ENGINE.

APPLICATION FILED MAR. 30, IBM.

Patented May 11, 1915.

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WitmeJ'ses: W4 WW B. V. NORDBERG.

VARIABLE CAPACITY COMPRESSED AIR ENGINE. APPLICATION FILED MAR. 30. 1914.

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THE NORRIS PETERS CO. PHOTO-LITHCL, WASHINGTON. D4 5.

United States BRUNO V. NORDBERG,

0F MILWAUKEE WISCONSIN.

VARIABLE-CAPACITY COMPRESSED-AIR ENGINE.

T all whom itmay concern Be it known that I, BRUNO V. NORDBERG, a citizen of the United States, residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented certain new and useful Improvements in Variable- Capacity Compressed-Air Engines, of which the following is a specification, reference being had to the accompanying drawing, forming a part thereof.

TlllS invention relates to compressed air engines of the type shown and described in Letters Patent No. 926,819, issued to me July 6, 1909, which are convertible from motors to compressors and vice versa, or to compressing engines of variable capacity, for handling negative loads or lowering loads. I

Its main objects are to increase the work of compression, to obtain at will a high mean effective pressure of compression without sacrificing or impairing the efliciency of compression, and to provide for a more effective, certain, accurate and economical control of the operation of engines of this class.

It consists in the construction, arrangement and combination of parts as hereinafter particularly described and pointed out in the claims.

For the purpose of illustration and eXplanation the present invention is shown and will be particularly described in connection with a convertible engine of the type above mentioned, although it may be applied to a compressor or air compressing engine employed solely for lowering loads either alone or in connection with a hoisting engine for lifting the loads.

In the accompanying drawing like characters designate the same parts in the several figures.

Figure l is a partial plan view of a convertible compressed air hoisting engine of the above mentioned type embodying the invention, part of the cylinder being broken away and shown in horizontal section; Fig. 2 is a side elevation thereof; Fig. 3 is a reverse side elevation of the cylinder showing a part of the valve operating mechanism directly connected with the by-pass valves; Fig. 4 is an enlarged view partly in elevation and partly in section of the automatic valve opening mechanism showing the same in inoperative condition; and Figs. 5, 6 and Specification of Letters Patent.

Application filed March 30, 1914.

Patented May 11, 1915. Serial No. 828,123.

7 are diagrams or representations of indicator cards illustrating the operation of the engine.

The engine which is shown and described 'n the above mentioned Letters Patent and to which the compression intensifying mechanism constituting the present invention is applied, is provided with means for convertmg it at wi and for varying its capacity as a compressor from zero to full capacity. By full capacity is here meant that corresponding with the piston displacement of the engine cylinder, the air being admitted at atmospheric pres sure. When such an engine operates as a compressor at full capacity its cylinder is filled with air at atmospheric pressure on each suction stroke of the piston, but as the cylinder has of necessity a certain amount of. clearance, that is, as there are always Waste spaces at the ends of the cylinder consisting of the space between the piston at the ends of its stroke and the cylinder heads and of the valve cavities, the air confined and compressed by the piston in these spaces and cavities will not be discharged under pressure into the receiver or reservoir, but will either be released and discharged back into the atmosphere when the suction valves open, or else will be expanded back in the cylinder to atmospheric pressure. The result as far as capacity is concerned, is the same in both cases. If the air from the clearance spaces is released and discharged back into the atmosphere (which will take place when the suction valves open on dead centers at the ends of the piston stroke) then this air is lost, so that the compressor actually delivers a quantity of air equal to its piston displacement minus the equivalent in free air of the quantity left in the clearance spaces which is discharged back into the atmosphere. The work of compression under these conditions is represented by the area abccl of the diagram or indicator card, Fig. 5, in which a-b is the compression line and 6-0 the discharge line. On the dead center at the end of the compression stroke of the piston designated 0, the pressure drops as represented by the line ccZ,' back to the suction pressure, which is ordinarily'that of the atmosphere. If on the other hand, the air in the clearance spaces is allowed to expand back to atmospheric pressure in the cylinder, as shown by the diagram or indicator card, Fig. 6, then the work necessary to compress the air in the clearance spaces is regained. In this diagram the line (e represents the clearance volume and the line c-f the piston displacement of the cylinder. The air is compressed as before, according to the line a,b, and discharged according to the line bc. In the clearance space is then left the volume of air represented by the line 0-6, the pressure of which is represented by the line eg. According to this method of operation the volume 0-6 of compressed air is allowed to expand on the suction or return stroke of the piston, as represented by the line c-h, the line g'h representing the volume which the air left in the clearance space at the end of the compression stroke of the piston occupies when it isexpanjdedrto atmospheric pressure.

At the point it the suction valveis opened and admits atmospheric air'into the cylinder during the remainder of the compressionior return stroke of the piston represented by the line h-0;. It will be apparent that the area a-b-ch corresponds exactly with the theoretical power required to compress the volume h-a, since the area-w-k-e- -g corresponds withthe work-required to compress the volume ag, while the area h-c eg corresponds with the work necessary to compress the volume gh.

It is manifest thatby the first method of compression, that is, if the air in the clearance space is discharged back into the atmosphere, only a quantity of air represented by the line a''h willbe compressed, while the work of compression is equal to that represented by the area a-b+c-0Z.

In practice the clearance volume e0 'is considerable, and if the initial pressure of the atmosphere is low, as will be the case when the engine .is located at a high altitude, then the volume of air compressed during the retardation periods of an engine of this kind such volumebeingrepresented by the linedh, Fig. 6) will be considerably less than the total piston displacement, and since the work of compression is'in proportion to the volume a-h compressed, it follows that at high altitudes the work of compression may be insufficient for retarding the engine withoutthe use of brakes.

Referring to the drawing, and particularly Fig. 1, in accordance with the present invention the ends of the engine cylinder 1 are connected by a by-pass 2, which is provided with a valve or valves 3, preferably two valves, one at each end of the by-pass, are employed, so that under ,normal working conditions the bypass does not form a part of the clearance space of the cylinder. These valves preferably close outwardly and their stems are connected by links with bell crank levers 4, which injturn are connected with each other by a double connecting rod 5, for simultaneously opening and closing the valves. The valves are closed by an adjustable spring 6, bearing at one end against a bracket 7 projecting from the cylinder and at the other end against a plate or seat on an adjusting screw 8 threaded in a cross piece between the two members of the connecting rod 5 and parallel therewith. At one end the rod 5 is connected by a link 9 with an arm 10 on a rocker shaft 11, extending across the cylinder at one end thereof and provided at its opposite end with an arm 12.

The by-pass valves 4: are brought into action and are automatically and momentarily opened on the dead centers of the engine or at the limits of the stroke of the piston whenever the maximum retarding power produced by the operation of the compression intensifying mechanism is required, as at the ends of hoisting periods when the engine is used to operate a. hoist, by mechanism which may be constructed substantially as follows: A cam 13 mounted on the crank shaft of the engine or on a lay shaft driven at the same speed as the crank shaft, is formed or provided on opposite sides with projections 14: adapted by engagement with a roller 15 carried by a three-armed lever 16, to rock said lever when it is released and held by a spring 17 in operative relation to the cam. Motion is communicated from the rocker lever 16 to the rocker shaft 11 bya rod 18, pivoted at one end to the arm 12 on said shaft and provided at the other end with a slotted head 19 adapted to be shifted at will into and out of engagement with said lever 16. The head 19 is shifted into and out of position to engage with the rocker lever 16 by a weighted lever 20 connected by a rod 21 with a lever 22, which'is in turn connected with a hand lever 23 on the operators platform. The operators lever 23 also has connections (not shown) for shifting the valve operating mechanism to convert the engine from a motor into a compressor-and vice versa, and for varying the driving power of the engine operating as a motor, and its retarding L power operating as a compressor. The construction and arrangement of the mechanism is such that a slight movement of the lever 20 is required to throw the compression intensifying mechanism into or out of action, and since this mechanism is required only at times when the engine is operating as a. compressor at fullnormal capacity, and the lever 23 servesalso to convert the engine from a motor into a compressor and vice versa, and to gradually vary its capacity both as a motor and as a compressor, a lost motion connection is interposed between it and the shifting lever 20. This lost motion connection may consist as shown in Figs. 2 and 4:, ofa slot in the head 24 of the connecting rod 21, engaging a pin on the lever 20. e

The slotted head 19 of the connecting rod 18 is provided with an adjusting screw 25 for engagement with an arm of the shifting lever 20, and the lever 16 is provided with a cross pin 26 for limiting the downward movement of the head 19 in position to properly cooperate with said lever 16 for opening the bypass valves 3. The lever 20 is provided with an adjusting screw 27, which by engagement with a stop 28, as shown in Fig. 4:, limits its movement when the hand lever 23 is turned back to its initial position, as indicated by a dotted line in Fig. 2, and the head 19 is lifted clear of the lever 16. When the compression in.- tensifying mechanism is thrown out of action by the lever 23, the rocker lever 16 is turned and held against the tension of the spring 17 out of position to work with the cam 13, by a piston 29 working in a cylinder 30 and provided with a rod 31 adapted when pressure is admitted to the cylinder, to engage with an arm of said lever and shift and hold the roller 15 out of the path of the projections 14 on said cam, as shown in Fig. 4. The cylinder 30 is connected below the piston 29 by a pipe 32, with a valve 33, as shown in Fig. 2. The valve 33 is operated by a connection with the lever 23, to admit compressed air or other fluid under pressure, to the cylinder 30 when said lever is in its initial position indicated by a dotted line, and to release the air or other fluid from the cylinder when said lever is shifted into position shown by full lines, for bringing the compression intensifying mechanism into action. A retracting spring 34 interposed between the piston 29 and the upper end of the cylinder 30, re turns the piston to its initial position, withdrawing the rod 31 from engagement with the lever 16 when fluid pressure is released from said cylinder. To enable the operator to open the by-pass valves 3 more or less, independently of the cam 13 at any point in the stroke of the engine piston, for the purpos of maneuvering in lowering and stopping a load, an arm 35 on the rocker shaft 11 is connected with a weighted foot lever 36 on the operators platform, by a rod 37 or other suitable connection. The rod 37 has a slotted connection with the arm 35 so as not to interfere with th action of the automatic valve opening mechanism when the rod 18 is operatively connected with the rocker lever 16.

In the operation of the engine, assuming that the piston is close to the limit of its movement to the right, as shown in Fig. 1, and that the by-pass valve operating mechanism is in the condition shown in Fig. 2, when the piston reaches such limit, all the ,mean effective pressure engine valves will be closed, the clearance space at the right hand end of the cylinder will be filled with compressed air, while the space on the other side of the piston will be filled with air at atmospheric pressure which has been drawn in through the suction valve during the now completed suction stroke of the piston. The valves 3 are now opened by the action of the cam 13 operating through the connections hereinbefore described, and communication being thus momentarily established between the ends of the cylinder through the bypass 2, the com pressed air in the clearance space at the right hand end of the cylinder is expanded into a space in the opposite end of the cylinder equal to that of the piston displacement of the cylinder plus twice the clearance space at one end of the cylinder. The pressure on the suction side of the engine now operating as a compressor is thus increased, and during the following compression stroke of the piston to the left the mean efof course be increased not only on account of the higher initial pressure of the air, but also because the work of expansion of the air in the clearance space in the right hand end of the cylinder (which would under normal conditions act as a driving force) now disappears.

Referring to Fig. 7, the shaded area fective pressure will abc-h, like the corresponding diagram or indicator card shown by Fig. 6, represents the compression of air during the normal operation of the engine working as a compressor at full capacity when the compression intensifying mechanism is inactive, while the area defined by the outside contour lines a-i-j-c/c represents the work performed when the initial pressure of the air to be compressed is increased by the action of the compression intensifying mechanism, as above explained. This diagram represents an actual case in which the atmospheric pressure is 12 pounds absolute at an elevation of approximately 6,000 feet above sea level.

It will be seen that the initial pressure is increased nearly 3 pounds, and that without the compression intensifying mechanism a of 25 pounds would be obtained, and with the intensifying mechanism in service, a mean effective pressure of 38.6 pounds is obtained. Therefore, when the intensifying mechanism is brought into action there is an increase in retarding force developed in the engine of over 50%.

In practice the intensifying mechanism is brought into action only at the end of hoisting periods, or when the engine is to be stopped, and since the action of this mechanlsm increases, the retarding force developed in the engine over 50%, its operation is required only for a few strokes of the piston.

With a compressed air engine of the convertible type to which the compression intensifying mechanism as herein describedis applied, the first movement of the hand lever 23 from its initial position indicated by dotted line in Fig. 2, to the left, applies the maximum driving power to the engine acting as a motor. By further 'move ment of the lever to the left, the driving or accelerating power is gradually reduced to zero, and at an intermediate point in the movement of the lever, the engine is converted from a motor to a compressor. The further movement of the lever from this position to the left, gradu ally increases the retarding power developed in the engine acting as a compressor from Zero to its full normal capacity, and then a slight further movement of the lever in the same direction brings the intensifying mechanism into action, thereby increasing theretarding power over 50%, as above explained.

Various changes in the details of construction and arrangement of parts of the intensifying mechanism and in the construction of the engine to which it is applied, may be made without departing from the principle and scope of the invention asdelined in the following claims.

I claim:

1. In a variable capacity compressed air engine the combination with a cylinder provided with a by-pass connecting the ends of the cylinder, of a valve controlling communication between the ends of the cylin der through the bypass, means for opening said valve at the limits of the piston stroke, and means for rendering said valve opening means operative at will.

2. In a variable capacity compressed air engine provided with means for varying its compressing capacity, the combination with the cylinder having a bypass connecting its ends, of a valve normally closing said bypass, means actuated by the engine and adapted to open said valve at the ends of the piston stroke, and means for rendering said valve opening means operative when the engine has reached its full compressing capacity working under normal conditions, to increase the work of compression.

3-. In a variable capacity compressed air engine adapted to be converted from a motor into a compressor at will and provided with means for varying its capacity as a compressor from zero to full capacity, the combination with a cylinder having a bypass, of a valve normally closing said bypass, means actuated by the engine for opening said valve at the limits of the piston stroke, and means for rendering said valve opening means operative when the engine has reached its full capacity working under normal conditions as a compressor, to

increase the work of compression.

4:. In a variable capacity compressed air engine the combination with a cylinder having a bypass connecting its ends, of valves controlling communication between the ends of the cylinder through the by-pass and located close to its ends, means tending to close said valves, automatic means adapted to momentarily and simultaneously open said valves at the limits of the piston stroke, and means for rendering said valve opening means operative and inoperative at will.

5. In a variable capacity compressed air engine the combination of a cylinder having a by-pass connecting its ends, a valve normally closing the bypass, means actuated by'the engineand adapted to automatically open said valve at the limits of the piston stroke, means for rendering said valve opening means operative or inoperative, and means for opening said valve at will and at any point in the piston stroke independently of said automatic means.

'6. In a variable capacity compressed air engine the combination of a cylinder having a bypass connecting its ends, a valve controlling communication between the ends of the cylinder through the by-pass, means tending to close said valve, a cam actuated by the engine and adapted to open said valve at the limits of the piston stroke, a lever adaptedto work with said cam, a connecting rod movable into and out of engagement with said lever, and a manually operated connection for shifting said connecting rod into and out of working position.

7 In a variable capacity compressed air engine the combination of a cylinder having a bypass connecting its ends, a valve normally closing said by-pass, means tending to close said valve, a cam actuated by the engine and adapted to open said valve automatically atthe limits of the piston stroke, a lever adapted to work with said cam for opening the valve, a spring tending to hold said lever in operative position relative to the cam, a connecting rod movable into and out of engagement with said lever, a fluid pressure motor for shifting and holding said lever out of operative position, and means for manually operating said valve and shifting said connecting rod into and out of engagement with said lever.

8. In a variable capacity compressed air engine the combination of a cylinder having a by-pass connecting its ends, a valve nor mally closing said by-pass, a cam actuated by the engine and adapted to automatically open said valve at the limits of the piston stroke, means for rendering said automatic valve opening means operative or inoperative at will, and a lever having a lost motion connection with the valve and adapted to open the same at will and at any point in the piston stroke independently of said cam.

9. In a variable capacity compressed air engine the combination of a cylinder having a by-pass connecting its ends, a valve normally closing said by-pass, means tending to close said valve, a cam actuated by the engine and adapted to open said valve automatically at the limits of the piston stroke, and a lever having a lost motion shifting connection with the valve opening means for rendering" said cam operative or inoperative.

10. In a variable capacity compressed air engine the combination of a cylinder having a by-pass connecting its ends, outwardly closing valves located at the ends of said by-pass, a connection for simultaneously opening said valves, a spring tending to close said valves, a cam actuated by the engine and adapted to automatically open the valves at the ends of the piston stroke, and means for rendering said cam operative or inoperative at will.

11. In a variable capacity compressed air engine the combination of a cylinder having a bypass connecting its ends, outwardly closing valves at the ends of the by-pass, bell crank levers connected with the valve stems, a rod connecting said levers, a spring acting on said rod and tending to close the valves, a rocker shaft connected with said rod, a cam actuated by the engine and adapted to open the valves at the limits of the piston stroke, a lever adapted to work with said cam for opening the valves, a rod connected with an arm on said rocker shaft and having a slotted head movable into and out of engagement with the cam lever, a lever for shifting said slotted head into and out of engagement with the cam lever, and means for manually operating said shifting lever.

In witness whereof I hereto afliX my signature in presence of two Witnesses.

E. G. BAYERLEIN, CHAS. L. Gross.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. 0. 

